Help with a crazy ***?

Basically I have a crazy stalker that I was friends with, can't handle her now. All she does is call me bawwing about relationship problems and how she thinks I'm not a good friend anymore, so I tell her I have to go, she also yells at me for sleeping when she calls at 2 am. I thought I'd finally gotten her to leave me alone because one of our mutual friends said she's livid with me and that I'd better stay away from her, in fact I went to my step sister's graduation, same grade as stalker, and she avoided me apparently, when she saw me she'd run. Afterwards she called me and bitched me out for not talking to her at graduation. Not only that but now she's demanding an apology because apparently I've been extremely mean to her, which she won't be getting. She said she won't talk to me until I apologize, but she keeps calling me still. Not only that I know for a fact she's sitting outside my house waiting for me to get home, luckily I loaned my car to a friend so they don't know I'm inside. WHAT SHOULD I DO!?